The RSO is made from a very brittle dark brown resin. Every time I pick it up a bit breaks off as you can see on the far side of the model where a bit of the fold down side is missing. It is inside the load deck. It has spent more time awaiting repair than any other model I have and you can see several joints.
A bit like the real thing I suppose. So to answer your question – I have no idea who made it though it is reasonably detailed.